Ukraine's interim prime minister meets with President Obama today at the White House. That visit comes at a time when Ukraine's territorial integrity is under threat. The country's region of Crimea is expected to vote this weekend to secede and join Russia. U.S. efforts to resolve this diplomatically with Moscow have gone nowhere. Now the Obama administration is trying to shore up the new government in Ukraine, and warning Russia that the annexation of Crimea will come at a cost.

JAY CARNEY: ...that we strongly support Ukraine, the Ukrainian people and the legitimacy of the new Ukrainian government.

KELEMEN: The Obama administration has been trying to draw Russia into negotiations with the U.S., Europe and Ukraine, but Russia refuses to accept what it calls a coup in Kiev, and has been consolidating its hold on Ukraine's Crimean peninsula. Seeing that, Secretary of State John Kerry sent a page and a half of questions to Russia to see if Putin is even interested in talks. His spokesperson, Jen Psaki, says the response from Moscow has been more of the same.

JEN PSAKI: There is an off ramp, here. We respect Russian interests, and as we have said all along, we respect the fact that Russia has interests, particularly in Crimea. But those interests, in no way, justify military intervention or the use of force.

KELEMEN: The White House says there will be costs to Russia, but that doesn't seem to have moved Putin, says Angela Stent, author of a new book about U.S.-Russian relations.

ANGELA STENT: It's clearly much more important for him to establish control over Crimea than the potential economic repercussions of sanctions. And I do think that some Russian officials really believe that the West has enough of an economic stake in Russia, that that restricts the degree to which sanctions are going to be imposed.

KELEMEN: She says the U.S. isn't going to war over Crimea, so may have to accept its annexation by Russia. But Adrian Karatnycky of the Atlantic Council points out that if Russia takes Crimea, it will be breaking international law and all the understandings that the Kremlin undertook with the collapse of the Soviet Union to respect the territorial integrity of other states. So he says it's time for a big think.

ANDREW KARATNYCKY: This is a landmark moment that will either change fundamentally the relationship of the West to Russia, or it will be business as usual and the encouragement of further such steps and further aggression. So I think it's a crucial moment in post-Cold War history.

KELEMEN: Karatnycky argues that the U.S. has said the right things, but needs to follow through and shore up Ukraine so it can deal with Putin.

KARATNYCKY: They have to, number one, deter Russia from further aggression with, I would say, aggressive sanctions and other means and diplomatic isolation internationally. And two, they have to help the Ukrainian state to stabilize itself through economic aid packages, and I would say also military assistance, technical assistance and the like.

KELEMEN: The E.U. is temporarily lifting tariffs on Ukrainian goods, and the U.S. has announced a billion dollars in loan guarantees. Both are encouraging Kiev to pursue reforms required by the International Monetary Fund for a larger bailout. Stent, who teaches at Georgetown University, says the White House needs to show Ukraine some tough love.

STENT: If they want to prevent any more erosion of their sovereignty, they have to move towards a more transparent, less corrupt, more effective government, and they really have to work hard.

KELEMEN: Ukraine's interim prime minister, Arseniy Yatsenyuk, is one of the leaders of the party set up by former prime minister and former political prisoner Yulia Tymoshenko, but he's not a charismatic politician like her. Instead, he's a technocrat with a steady hand, according to the Atlantic Council's Karatnycky.

KARATNYCKY: Yatsenyuk is a nerdy, technocratic moderate, who, you know, was head of Central Bank. He actually was once deputy governor of Crimea. He's a career administrator.

KELEMEN: And that could be key, as he negotiates with the IMF and tries to stabilize Ukraine's fragile economy.